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If its L jet expertise you need you might think about tapping the 944 crowd as they are pretty much all L-jet. It there still a big 944 racing class? You could either tap into 944 racing class or 944 forum here on the list.
I don't think L jet brain failure is common, but anything is possible. You might want to put a plug out where you can see the spark, just to confirm. If you have a nice spark, I think you can totally rule out the green wire. Then, I would use a 'noid light rather than listening for injectors. You can rent a 'noid light kit for free at O'Reilly and probably at Autozone. L jet is pretty simple: The dist/green wire creates a pulse that goes to the injectors. The pulse gets stretched out in length depending on engine temp, air temp, and the AFM reading. If you can get the pin-out you can see what the air temp, engine temp, and AFM readings look like right at the computer.
Thanks.. and yes, we are getting a good spark coming from the cap / and plug wires as well as the plug. those injectors make a lot of noise with a stethoscope and they are dead.... nothing.. no gas smell either. if there was gas, there would be something firing.
the 944 is close, but I think its motronic or something slightly different. however, I will see if there is something they might be able to help with .
one thing that is a concerning indication is that the tach is not registering anything as it is being turned over. that's what made me think its something coming from the tach to the Ljet that is not giving the signal which might be needed for injector firing.
Here's the wiring diagram for an '82 Ljet. Really simple. Injectors on top, sensors on the bottom. One thing you can do is look to see if the relay it turning on. If it is, one side of the each injectors should have 12V. The computer fires the injectors by pulling the other side to ground. If the relay is on but injectors not firing, both sides of each injector will be 12V.
-- signal from distro via green wire is critical to having spark, and for generating the tach pulse signal used by the tack and the fuel pump relay.
-- You say you have spark at the cap, so distro is turning and signal makes it to the spark box. If the timing is OK (check with light while cranking), the green wire is OK and you can move on.
-- You say injectors are clicking with a stethoscope, so it sounds like the LJET box is working.
-- You say that there's no fuel smell. That may be the clue that points to a failed fuel pump relay, failed fuel pump, or no gas in the tank.
-- Is there any/good gas in the tank? (if not, now would be a good time to add some...)
-- Can you hear the fuel pump running by the tank while cranking? (takes two people...) If not, temporarily jumper the fuel pump relay and see if the pump runs. If it does, replace the relay. If it doesn't, trace power starting at the fuse holder, going both ways (to battery, to pump relay socket, to pump)
-- If pump runs, do you have fuel pressure with pump relay jumpered?
Redneck troubleshooting: Spray some fuel into the intake at the airflow meter, and crank the car. If it sputters and tries to run for a few seconds, your problem is fuel system related. If nothing, go back to verifying spark at a plug, timing, tach moving on cranking, then pump relay getting a tach signal (31b pulls towards ground -- look at it with an analog (needle type) voltmeter or your oscilloscope), and work back towards ignition if no pulse, forward through fuel relay and pump system if pulses but no relay close/pump run. Troubleshooting is a divide-and-conquer exercise. Test somewhere in the middle and work your way towards the end where you find the works/doesn't work boundary.
Here is the ignition circuit. The heavy line with the dashed line on both sides is the green wire. You can see that it goes to the ignition box, but then it is also relayed on by the ignition box. Cannot read the pin number on this schematic, but it is the only signal coming out the top of the ignition box on this diagram. That signal is what goes on to trigger the Ljet ,run the tach, and enable the fuel pump. I'm guessing that is where your trouble is. Could be:
-signal is just not coming out of ignition box-bad ignition box
-a short to ground somewhere on that signal
-the signal path is broken
I would tend to guess the last, and want to have a look at the connection where the signal from the ignition box enters the central electrical cluster. Again cannot quite read it from this schematic, but it looks like maybe 07 or Q7 or something.
Yes and the signal from the ignition box to the Ljet goes through the big engine bay harness to the central panel and thence to the Ljet. So another quick thing to do amid your other troubleshooting is pull off and push back on the colored connectors at the central panel. I’d have to check which ones exactly but the main harness starts at M, I think, and goes to about U. The Ljet is X as I recall. Just pull them all off and plug back in to let them self clean.
Hi Bob!! thanks good info.....you might have missed it, I DONT hear any thing on the injectors... no fuel smell, so I think for some reason, the injectors are not firing. sounds like if I have spark, the green wire, is providing a signal that is being received by the Ljet and the ignition box, but not registering on the tack. I would think it would move a little and doesn't, also, the fuel pump relay is engaging! so, no issues there and we have fuel pressure. however, we didn't verify that the pump relay is running while turning over.... it primes with ignition (for SURE its running via ignition key turn) .... and I think we hear it running after turn off. (I don't remember)…
Mark
Originally Posted by dr bob
Mark --
Basics:
-- signal from distro via green wire is critical to having spark, and for generating the tach pulse signal used by the tack and the fuel pump relay.
-- You say you have spark at the cap, so distro is turning and signal makes it to the spark box. If the timing is OK (check with light while cranking), the green wire is OK and you can move on.
-- You say injectors are clicking with a stethoscope, so it sounds like the LJET box is working.
-- You say that there's no fuel smell. That may be the clue that points to a failed fuel pump relay, failed fuel pump, or no gas in the tank.
-- Is there any/good gas in the tank? (if not, now would be a good time to add some...)
-- Can you hear the fuel pump running by the tank while cranking? (takes two people...) If not, temporarily jumper the fuel pump relay and see if the pump runs. If it does, replace the relay. If it doesn't, trace power starting at the fuse holder, going both ways (to battery, to pump relay socket, to pump)
-- If pump runs, do you have fuel pressure with pump relay jumpered?
Redneck troubleshooting: Spray some fuel into the intake at the airflow meter, and crank the car. If it sputters and tries to run for a few seconds, your problem is fuel system related. If nothing, go back to verifying spark at a plug, timing, tach moving on cranking, then pump relay getting a tach signal (31b pulls towards ground -- look at it with an analog (needle type) voltmeter or your oscilloscope), and work back towards ignition if no pulse, forward through fuel relay and pump system if pulses but no relay close/pump run. Troubleshooting is a divide-and-conquer exercise. Test somewhere in the middle and work your way towards the end where you find the works/doesn't work boundary.
Last edited by mark kibort; 11-19-2019 at 05:26 PM.
I found the L jet very reliable.....the Estate ran it for years with minimal issues.
It might not be your cause, but one thing I found with L jet is all the different values for the air flow meter are VERY important. The estate was running poorly and everything else checked out. One of the 5 pins at L jet brain were slightly incorrect values...only a like a hundred ohms if I remember right. Put a rebuilt AFM from Anderson and pack to running perfect.
The green wire is a likely cause for your issue.....since you have spark I doubt its the resistors under the coil
Check for battery voltage at pin 30 of the AFC relay with the relay installed. You want to look while cranking if you can. Should be battery voltage. You can test at V4 and just leave the relay in place. If not battery voltage, look at the dedicated fuel injection feeder at the positive battery terminal. There is no fuse in this circuit.
Check for battery voltage at W2 through W5 (any of them...) with key in engine run position. You should hear the relay close when key transits to run. Crank the starter while testing again, and verify that battery voltage is maintained. If not or a lot of drop, replace the AFC relay at XVI. test again.
The injection system works with battery voltage on one side while the AFC relay is closed (key in run or start). Ignition pulses (via tack signal) cause the control unit to pull the other side of each injector coil towards ground. The cycle time is a function of seeing air flow at the AFM, then the pulse on time is based on measured airflow volume and the measured air temperature to calculate mass flow. You can use a noid light at each injector to see if you are getting pulses, and a voltmeter at any injector to confirm battery voltage with a meter on the red/black and red/green. Use an analog meter or your oscilloscope to watch voltage on the controller side of the injectors, the green, green/black, gray/green, green/red wires depending on which injector. Voltage should swing between battery voltage and a little less than 1 Volt while cranking.
Ok, we used the starter fluid and got the engine to try and start.. so , looks like the ignition is working fine and we got a read from the TACH too, so that's good. fuel pump relay is running, and continues to run after key turns off by a second or two.. you mentioned the AFC relay (I called it the EFI relay) and we changed that out and that's how we got the fuel pump to run with the key starting the car, and the relay itself would click... ((didn't before) we thought that was the issue, but it wasn't. it looks like we have narrowed this down to the fuel system at the brain. or those connectors at the bottom...… im thinking we get the brain from mark anderson, if I cant get something to change by removing and reconnecting those lower multi wire connectors from the harness.
thanks for all the suggestions!
Mark
Originally Posted by dr bob
Mark --
Check for battery voltage at pin 30 of the AFC relay with the relay installed. You want to look while cranking if you can. Should be battery voltage. You can test at V4 and just leave the relay in place. If not battery voltage, look at the dedicated fuel injection feeder at the positive battery terminal. There is no fuse in this circuit.
Check for battery voltage at W2 through W5 (any of them...) with key in engine run position. You should hear the relay close when key transits to run. Crank the starter while testing again, and verify that battery voltage is maintained. If not or a lot of drop, replace the AFC relay at XVI. test again.
The injection system works with battery voltage on one side while the AFC relay is closed (key in run or start). Ignition pulses (via tack signal) cause the control unit to pull the other side of each injector coil towards ground. The cycle time is a function of seeing air flow at the AFM, then the pulse on time is based on measured airflow volume and the measured air temperature to calculate mass flow. You can use a noid light at each injector to see if you are getting pulses, and a voltmeter at any injector to confirm battery voltage with a meter on the red/black and red/green. Use an analog meter or your oscilloscope to watch voltage on the controller side of the injectors, the green, green/black, gray/green, green/red wires depending on which injector. Voltage should swing between battery voltage and a little less than 1 Volt while cranking.
Mark, check fuel pressure and delivery volume per the WSM procedure and specs. Storage is much more likely to affect pump and FPR performance than the brain.
We too often jump to the most-expensive but low-probability causes. Simple stuff is he most likely. Test and analyse instead of throwing parts and money at something.
Bob, I get that.. but we have NO injector firing.. it is easy to test with a stethoscope. we have fuel pressure, the injectors are not firing they make a distinct clicking noise. I have such sensitivity, is when the car is turned on , I can hear a high pitch electrical whine at the injector.
if it was firing, it would be very obvious. we have fuel pressure so if we have pressure , the injector firing is the issue. how can we investigate this?
Originally Posted by dr bob
Mark, check fuel pressure and delivery volume per the WSM proceure and specs. Sorage is much more likely to affect pump and FPR performance than the brain.
We too often jump to the most-expensive but low-probability causes. Simple stuff is he most likely. Test and analyse insstead of throwing parts and money at something.
noid light and dmm. Isolate the injector sections (4 groups of two injectors), and test for open, impedance and ground on each section. Ifthe harness sections are OK and not grounded or shorted, verify the ground for the controller. The LJET controllers are pretty bulletproof. Get a controller to test in the car, if it's handy.
just switched the Ljet computer brain and no difference. runs with a little starter fluid, no problem with both brains. no clicking noise coming from the injectors. these things make a racket if you have a stethoscope.. thinking it on to the next fault point.
so we have spark. it runs on starter fluid, but no injectors are firing. tach working too. any ideas??? what the heck could it be???? after all this was a running car. nothing happened but sitting for a long time. so it must be a corroded connection???
Since it runs on starter fluid, and tach works then, you have confirmed the green wire is not the issue. You have stated that you have fuel pressure, and the pump now runs after replacing relay XVI. It was a little confusing in some of your posts, but I see you saying now the injectors are NOT making any noise. They certainly don't appear to be firing. Have you confirmed 12V going to the injector plugs? Both sides should have 12V with the key on until they fire. If not look at relay XVII. You replaced relay XVI. XVII is the fuel injection relay. [EDIT: WRONG...XVI powers the injectors.]
just switched the Ljet computer brain and no difference. runs with a little starter fluid, no problem with both brains. no clicking noise coming from the injectors. these things make a racket if you have a stethoscope.. thinking it on to the next fault point.
so we have spark. it runs on starter fluid, but no injectors are firing. tach working too. any ideas??? what the heck could it be???? after all this was a running car. nothing happened but sitting for a long time. so it must be a corroded connection???
Mark, read post 27. You need a Noid light and your DMM to diagnose.
Isolate each pair of injectors at the harness connectors (not at the injectors) so you can test them as pairs with wiring. In parallel, the injectors will show 1/2 the resistance as a single injector. If less, you have a short. If more, you have an open. If infinite, inspect the harness and the injector connectors. Test both leads resistance to ground, should be infinite. There are four pairs of two injectors, so you'll test each pair separately.
FWIW, you have the symptoms of rodent damage in the engine bay. Mice love to chew on wiring for some reason. With everything connected and in parallel, it only takes one shorted wire pair to doom all the injectors. The DMM is your friend, from the harness connector ends.
11-19-2019, 03:27 AM
